Apparatus for checking the correct operation of speed responsive devices for engine fuel systems



Nov. 19, 1968 E. H. WARN'E 3,411,290

APPARATUS FOR CHECKING THE CORRECT OPERATION OF SPEED RESPONSIVE DEVICES FOR ENGINE FUEL SYSTEMS Flled March 20, 1967 United States Patent 3,411,290 APPARATUS FOR CHECKING THE CORRECT OPERATION OF SPEED RESPONSIVE DE- VICES FOR ENGINE FUEL SYSTEMS Eugene Harold Warne, Solihull, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England, a British company Filed Mar. 20, 1967, Ser. No. 624,439 Claims priority, application Great Britain, Mar. 24, 1966, 13,118/ 66 3 Claims. (Cl. 60-3928) ABSTRACT OF THE DISCLOSURE Apparatus for use with a gas turbine engine having two independently rotatable concentric shafts comprises a pair of speed responsive devices driven by the engine shafts respectively, these devices producing signals applied to a valve actuating member through a first diaphragm to control fuel flow to the engine from a pump through a servo device, there being manually controllable valve means whereby the signal pressures can be applied to the valve actuating member through a second diaphragm so that the valve will be actuated, for test purposes, at a substantially reduced speed.

This invention relates to apparatus of the kind for use in conjunction with gas turbine engines having two independently rotatable concentric shafts, normally though not always carrying respective compressors and turbines, said apparatus including a pair of speed responsive devices responsive to the speeds of the shafts respectively, said devices being arranged to provide signals applied to apparatus for controlling the supply of fuel to the engine. I

The object of the present invention is to provide such apparatus in a form in which tests can be made to ensure correct operation.

In accordance with this invention, apparatus of the kind specified for use with a gas turbine engine comprises a pump, a servo device for controlling the pump output, a valve actuated by a biased actuating member, said valve being arranged to control the servo device, said valve actuating member being responsive to said signals, and a manually controllable valve means which in a predetermined position, is arranged to modify the effect of the signals upon the valve actuating member in such manner that the valve can be actuated to test its operation at a substantially reduced speed.

The invention will now be described by vvay of example with reference to the accompanying drawings in which:

FIGURE 1 illustrates diagrammatically part of a fuel system for use with a gas turbine engine, and incorporating apparatus constructed in accordance with this invention, and

FIGURES 2 and 3 illustrate alternative positions of valves in the apparatus.

The apparatus shown comprises an engine driven fuel pump v which obtains a supply of fuel from a reservoir (not shown) through a line 11, the supply of fuel being pressurized by a boost pump 12 and being filtered by the device indicated generally at 13. The pump 10 is of the swash plate type and has a servo device 14 for varying the swash plate angle, and there is a delivery passage 15 from the pump leading through a fuel/air ratio control device (not shown) and a throttle (not shown) to burners in the engine. The pump 10 is driven by a shaft 6 which also drives a speed responsive device 17 com. prising a rotor within which is disposed a valve closure Ice member 18, the rotor being disposed in a chamber 19 in a body 16- which also houses the pump 10. The device 17 produces a pressure signal in a passage 23 which leads from the chamber 19, this signal being dependent upon speed.

The engine is of the kind in which there are two concentric shafts carrying respective compressors and turbines, one of the engine shafts driving the shaft 6 of the pump 10, and thus driving the speed responsive device 17.

The other engine shaft drives a shaft 20' which carries a further speed responsive device indicated generally at 21, and disposed within the chamber 22. These two devices 17 and 21 are of a similar nature and are arranged to supply through respective passages 23, 24, fluid pressure signals to opposite sides respectively of a diaphragm 25 carrying a closure member 25a which can engage with respective seatings 26, 27. There is a pressure operable valve 30 which is arranged to raise the signal derived from the device 21 to an extent to ensure that the pressures in the passages 23, 24 are approximately of the same order. Fuel can be supplied by means of this apparatus, at the higher of the two signal pressures, to a passage 28 leading to a compartment 29 in the body 16.

This arrangement is fully described in the complete specification of our copending British patent application No. 13,117/66.

The chamber 29' in the body 16 is divided into three portions by two diaphragms 31, 32, the latter being the larger, these two diaphragms being carried by a valve actuating member 33 to which is connected an adjustable tension spring 34. The opposite end of the valve actuating member 33 from the spring 34 is arranged to act against a valve closure member 35 for controlling the flow of fuel from one side of the servo device 14, the valve closure member 35 being loaded in a closed direction by a spring 36.

In normal use, one side of the smaller diaphragm 31 in the chamber 29 is subjected to the higher of the two signal pressures through the passage 28, whilst the other side is subjected to the pressure at the inlet of the pump through a passage 37, both sides of the langer diaphragm 32 being subjected to the latter pressure through a loop passage 38, 39.

In the passages 28 and 38, 39 there are respective valves 40, 41 which are arranged to be manually controlled in unison, and in the position shown in FIGURE 1 fluid flow can take place through the passages in order to subject the smaller diaphragm 31 to the respective pressures referred to. If the two valves are moved to the position shown in FIGURE 2, both sides of the smaller diaphragm 31 are subjected to the signal pressure derived from the speed responsive device 21 and exerted through the passage 24. The langer diaphragm 32 is now subjected to the signal pressure from the speed responsive device 21 on one of its sides and the inlet pressure of the pump at the other side. Since the diaphragm 32 is larger than the diaphragm 31 the value of the signal from the device 21 which will operate the valve closure member 35 will be considerably lower than that which will operate it when the smaller diaphragm 31 is subjected to the signal pressure and to the pump inlet pressure respectively. In this way a test can be made to ensure correct operation of the speed responsive device 21 to actuate the valve closure member 35 at a lower engine speed than is the case when the signal pressure is applied to the smaller diaphragm 21.

When the valves 40 and 31 are turned to the position shown in FIGURE 3, the other of the two signal pressures from the device 17 is applied to both sides of the smaller diaphragm and therefore this signal pressure is applied to one side of the diaphragm 32 whilst the other side is subjected to pump inlet pressure. This signal pressure from the device 17 is applied through the passages 44- and 45. In this way the correct operation of both the speed responsive devices 17 and 21 can be tested without engine speeds in the higher operating ranges being achieved.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. Apparatus for use with a gas turbine engine having two independently rotatable concentric shafts, comprising a pair of signal producing speed responsive devices responsive to the speeds of the shafts respectively, a device to which said signals are applied for controlling the supply of fuel to the engine, a fuel pump, a servo device for controlling the pump output, a valve closure member and actuating member therefor responsive to said signals for controlling the servo device and manually controllable valve means which in a predetermined position, arranged to modify the eifect of the signals upon the valve actuating member in such manner that the valve closure member can be actuated to test the operation of the speed responsive devices at a substantially reduced speed.

2. Apparatus as claimed in claim 1 in which the valve actuating member is responsive to said signals which are in the form of fluid pressures, through a first diaphragm to which, at any operating condition, a selected one of the signals is applied, the valve actuating member being biased in a direction in opposition to the force provided by said signal, said manually controllable valve means being arranged in said predetermined position to apply said selected signal pressure to a second diaphragm of larger area and also connected to the valve actuating member, meanwhile ensuring opposite sides of the first diaphragm are in communication with one another.

3. Apparatus as claimed in claim 2 in which said manually controllable valve means can occupy a further position in which the other of said signal pressures can be applied to said larger diaphragm instead of said selected one of the signal pressures.

No references cited.

JULIUS E. WEST, Primary Examiner. 

